perf: respect django database routing

[systemime]

Summary:

• Celery Version: 5.1.2
• Celery-Beat Version: 2.2.1

The problem you want to solve

If the django project is configured with multiple databases, the default behavior in the django-celery-beat will cause django to get the default database connection, but at this time it is an empty dictionary, and then a database configuration exception will be thrown. This pr will check the DATABASE_ROUTERS to determine whether django db router is needed.

[auvipy]

can you also add relevant test ?

[auvipy]

@D3X @lvelvee can you try this pr to verify it won't introduce any regression?

[systemime]

Sorry, I'm trying to add unit tests for here but don't have any good ideas. I referenced Django's unit tests and used the override_settings decorator to simulate the multidb case. By default, the Router's db_for_write method returning None will cause Django to use the default database configuration, regardless of whether the user is using multidb or not.

@auvipy

[auvipy]

using django unit test is a good start, I will take some time to properly review & test it before merge

[auvipy]

tests are failing. also please rebase

[auvipy]

I tried to rebase and fix the conflicts to see where it stands right now

[Copilot]

Pull Request Overview

This pull request improves Django database routing support for django-celery-beat by ensuring the proper database connection is used when multiple databases are configured.

• Adds a Router class and overrides DATABASE_ROUTERS in tests to simulate different routing scenarios.
• Adapts transaction handling in schedulers to commit and run within the correct database using a new target_db property.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
t/unit/test_schedulers.py	Updates tests to include DATABASE_ROUTERS and ROOT_URLCONF overrides for simulating routing.
django_celery_beat/schedulers.py	Adds a target_db property and updates transaction handling to respect the correct database.

[auvipy]

=========================== short test summary info ============================
FAILED t/unit/test_schedulers.py::test_modeladmin_PeriodicTaskAdmin::test_run_task
!!!!!!!!!!!!!!!!!!!!!!!!!! stopping after 1 failures !!!!!!!!!!!!!!!!!!!!!!!!!!!
============ 1 failed, 70 passed, 13 warnings in 143.04s (0:02:23) =============
py312-django42: exit 1 (143.99 seconds) /home/runner/_work/django-celery-beat/django-celery-beat> pytest -xv --cov=django_celery_beat --cov-report=xml --no-cov-on-fail --cov-report term pid=3348
py312-django42: FAIL code 1 (153.77=setup[9.63]+cmd[0.15,143.99] seconds)
evaluation failed :( (153.91 seconds)